Remote surveillance devices have a variety of uses. They are used when the observation site is too dangerous or is inaccessible to a human observer, or when a number of sites must be watched by a lesser number of observers. In many situations passive type systems are preferred, particularly when hostile personnel are being studied. As the available ambient light diminishes due to the rotation of the earth or weather conditions, these systems become less effective and sometimes useless. Since the infrared (IR) region provides the most reliable light source under low light level conditions, most sensing systems use detectors which are sensitive to that region of the spectrum. This affords the user an opportunity to use artificial illumination which cannot be seen by the naked eye. However, to use such illumination continuously would be wasteful and sometimes dangerous. By limiting its use only those times when it is actually needed, the drain on the remote systems is minimized and such systems can, in some cases, employ inexpensive photocells to charge the batteries when ambient radiation is high.